My "favorite" (if you can call it that) is Mistake 2: Absolute URLs mistakenly written as relative URLs. It's too easy to make if you're not thinking carefully about what you're typing, even if you're a very experienced web dev or SEO, and sometimes beginners find the subtlety involved hard.﻿

I have a question that isn't covered in the article. What if the rel="canonical" tag targets an URL that redirects to another URL? Will Google ignore the tag, or accept the URL resulting from the redirection? We're assuming the pages involved are actually duplicated.﻿

Hi +Evan Hall. That's a more complex situation as now we're talking about at least 3 URLs, and potentially more, in a canonicalization "chain". The canonicalization signals are still considered as usual, i.e the rel="canonical" and the redirect are still taken into account.﻿